Range hood capable of resisting draft

ABSTRACT

A range hood capable of resisting draft is provided above a counter on the top of which an air-generation device is located. The range hood comprises an air-extraction hood that has a bottom provided with an elongate air-extraction slot for drawing air upwards. Besides, an air blow groove is provided in front of the elongate air-extraction slot for blowing air downwards. A long left upright plate and a long right upright plate are respectively provided below the left and right lateral surfaces of the air-extraction hood. Thereby, when the elongate air-extraction slot draws in air, an oblique airflow is formed. Besides, the long left and right upright plates are able to hinder the draft coming from lateral sides, so as to protect the oblique airflow structure. Consequently, an intact upwards-flowing airflow is formed to exhaust soot and harmful gases.

TECHNICAL FIELD

The present invention relates to a range hood, and more particularly, to a range hood which is capable of resisting the draft coming from all directions and exhausting soot and pollutants, and is suitable for household kitchens, kitchens of restaurants, or other working places producing polluting gases.

BACKGROUND

A conventional range hood in a kitchen scarcely differs from a top-suction style range hood in a working space. In this conventional kind of range hood, the velocity of airflow flowing upwards is much decreased when the airflow is approaching the air-extraction slot of the range hood in a short distance, and thus the upward extraction force is usually insufficient. Thereby, the performance of the range hood is much easily liable to the draft caused by people walking by, fans, or the operation of air conditioners. As a result, the effective area for confining soot is greatly reduced to a small area. In this way, the soot when being closely adjacent to the air-extraction slot will escape along with the draft, which will jeopardize the health of those who cook in kitchens.

Consequently, in order to overcome above problem, the inventor has developed a range hood having “air curtain” based on aerodynamic principles. The main technical feature of above range hood is to provide an air jet blown in a upward and oblique direction in front of a counter, and provide a air-extraction hood in the shape of a slot above an oven, where the left and right sides of the oven on the counter are left open for the purpose of air supply, so as to form a nearly two-dimensional air curtain by means of the blown and drawn air jets. This flow field conforming to aerodynamic principles is able to have the soot and harmful gases between the oblique air curtain and a rear wall be carried steadily upwards to the air-extraction hood and exhausted.

In implementation, without strong draft, above range hood is indeed capable of confining and exhausting the soot and harmful gases effectively. Besides, it is able to minimize the leakage caused by people walking by or by slight draft with velocity below 20 cm/s. As mentioned above, the left and right sides of the oven on the counter are left open and air can be drawn in and supplied so as to form a two-dimensional air curtain facing those who are cooking. In this way, it is able to provide a strong resistance against the interference of the draft in front of the counter. However, in kitchens, it is quite difficult to completely get rid of the interference of slightly stronger draft coming from all directions, such as the airflows produced by electrical fans or others flowing through door or window from without. This phenomenon will complicate the draft in the kitchens. Particularly, when the draft exists near the left and right sides of the oven on the counter, air curtain structure will be destroyed by the draft coming from lateral sides through the air supply spaces formed near the left and right sides of the oven on the counter. Consequently, it may greatly reduce the ability of exhausting soot. According to the results from the experiments conducted in National Taiwan University of Science and Technology, when the velocity of draft is more than about 20 cm/s, serious leakage of soot may occur in commercially available conventional range hoods. This phenomenon will also occur in range hoods having two-dimensional air curtain. Draft is commonly found in kitchens and its velocity is difficult to be confined within a small range. Thereby, the leakage of soot is quite serious in these places. Besides, when the soot and gases are of high temperature, it is even more difficult to prevent the leakage of soot due to the expansible characteristic of gases.

Moreover, above range hood having two-dimensional air curtain is required to include simultaneously an air blow device and an air-extraction device. Therefore, it is quite inconvenient to assembly or to replace these components. Besides, since more apparatuses are required, the cost of apparatuses and labor is thus increased.

In order to provide an improved structure distinct from conventional ones and overcome above shortcomings, inventor had the motive to study and develop the present invention. After hard research and development, the inventor provides a range hood that is capable of resisting draft coming from all directions and of preventing the leakage of high-temperature expanding gases, so as to exhaust effectively soot and harmful gases.

SUMMARY OF THE DISCLOSURE

An object of the present invention is to provide a range hood capable of resisting draft, where by providing an elongate air-extraction slot on the bottom of the air-extraction hood and providing a long upright plate respectively below the left and right lateral surfaces of the air-extraction hood, it is able to prevent lateral draft from flowing in and to form an intact upwards-flowing airflow, so as to exhaust soot and harmful gases.

Another object of the present invention is to provide a range hood capable of resisting draft, where by providing a long upright plate respectively below the left and right lateral surfaces of the air-extraction hood and providing a guiding structure respectively at the front ends of the two upright plates, when air is drawn into the space below the air-extraction hood through the front ends of the upright plates, it is able to reduce the backflow areas formed by the deviated airflow from the front ends of the left and right upright plates, so as to keep the exhaust airflow flowing smoothly.

Another object of the present invention is to provide a range hood capable of resisting draft, where by providing an air blow groove at one end of the air-extraction slot located on the bottom of the air-extraction hood, the upwards blown air can confine the high-temperature expanding gas produced by an air-generation device and guide the high-temperature expanding gas into the elongate air-extraction slot in order to prevent its leakage.

In order to achieve above objects, the present invention provides a range hood capable of resisting draft, a back of which is disposed onto a wall and is located above a counter, where an air-generation device is provided on the counter's top. The range hood comprises an air-extraction hood, a long left upright plate, and a long right upright plate. The air-extraction hood has a bottom provided with an elongate air-extraction slot having an opening that faces downwards. The elongate air-extraction slot is in communication with an air-extraction device for drawing air upwards. The elongate air-extraction slot has a front end provided with an elongate air blow groove having an opening that faces downwards. The elongate air blow groove is in communication with an air blow device for blowing air downwards. The elongate air-extraction slot and the elongate air blow groove are provided between the front end surface and the rear end surface of the air-extraction hood and are parallel to the front end surface and the rear end surface. The long left upright plate is fixedly provided below a left lateral surface of the air-extraction hood, where the horizontal width of the long left upright plate is no less than the horizontal distance from the rear end of the air-generation device to the wall, while the vertical length of the long left upright plate is no less than the height from the counter's top to a bottom of the long left upright plate. The long right upright plate is fixedly provided below a right lateral surface of the air-extraction hood, where the horizontal width of the long right upright plate is no less than the horizontal distance from the rear end of the air-generation device to the wall, while the vertical length of the long right upright plate is no less than the height from the counter's top to a bottom of the long right upright plate.

In implementation, a curved first guiding part is provided at a right side of the front end of the left upright plate, and a curved second guiding part is provided at a left side of the front end of the right upright plate

In implementation, when the range hood capable of resisting draft is directly hung above a counter, the elongate air-extraction slot is located in the midway between a front end surface and a rear end surface of the air-extraction hood. The horizontal width of the long left upright plate is no less than one-fourth the horizontal width of the left lateral surface of the air-extraction hood, and the horizontal width of the long right upright plate is no less than one-fourth the horizontal width of the right lateral surface of the air-extraction hood, so that they are able to cover the left and right lateral surfaces of the air-generation device. Moreover, the front end and the rear end of the elongate air-extraction slot are respectively provided with an elongate air blow groove having an opening that faces downwards. The elongate air blow groove is in communication with an air blow device for blowing air downwards. Besides, the air blow groove is parallel to the elongate air-extraction slot.

The following detailed description, given by way of examples or embodiments, will best be understood in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a first embodiment of the present invention, which is disposed above a counter.

FIG. 2 is a cross-sectional view showing the first embodiment of the present invention, which is disposed onto a wall.

FIGS. 3 and 4 is a cross-sectional view showing an air collector of one shape according to the present invention.

FIGS. 5 and 6 show the use of the first embodiment of the present invention in the exhaustion process of gases.

FIG. 7 shows the use of a second embodiment of the present invention in the exhaustion process of gases.

FIG. 8 is a cross-sectional view showing a third embodiment of the present invention.

FIG. 9 shows the use of the third embodiment of the present invention in the exhaustion process of gases.

FIG. 10 is a comparison curve graph showing the capture efficiency obtained respectively after the present invention and other range hood are given a static test.

FIG. 11 is a comparison curve graph showing the capture efficiency obtained respectively after the present invention and other range hood are given a dynamic test.

FIG. 12 is a cross-sectional view of a fourth embodiment of the present invention, which is disposed onto a wall.

FIG. 12A is a perspective view showing another pattern of an air blow groove in the fourth embodiment of the present invention.

FIG. 13 shows the use of the fourth embodiment of the present invention.

FIG. 14 is a cross-sectional view of a fifth embodiment of the present invention.

Attachment 1 is a picture showing the smoke in a horizontal plane and an intermediate vertical plane, where the present invention releases smoke above an oven and adopts a technique by using laser to visualize the flow field of the smoke.

DETAILED DESCRIPTION

Please refer to FIGS. 1-2 showing a first embodiment of a range hood 1 capable of resisting draft according to the present invention. In this embodiment, the range hood has a back disposed onto a wall 11 and is located above a counter 12. An oven is provided on the top of the counter 12, and above the oven cookware can be placed. The oven is designed to be an air-generation device 13. The air-generation device has a rear end 131 facing the wall 11 and a front end 132 that is opposite to the rear end 131 and away from the wall 11. In implementation, the air-generation device 13 also can include a cookware or other utensils capable of producing harmful gases. Besides, the range hood 1 comprises an air-extraction hood 2, a long left upright plate 3, and a long right upright plate 4.

The air-extraction hood 2 has an air collector 21. The air collector 21 is a substantially rectangular casing having a space 211 therein. Besides, the air collector 21 has a bottom plate 212 that is provided with an elongate air-extraction slot 22 having an opening that faces downwards. The elongate air-extraction slot 22 is located between a front end surface 23 and a rear end surface 24 of the air-extraction hood 2 and is parallel to the front end surface 23 and the rear end surface 24. The bottom plate 212 of the air collector 21 is provided with an oil barrier frame 213. The oil barrier frame 213 protrudes from the surface of the bottom plate 212 and encircles the peripheries of the elongate air-extraction slot 22. An oil storage box 25 is provided below the rear end of the surface of the bottom plate 212 of the air collector 21. Alternatively, the oil storage box 25 also can be provided below the front end or below the lateral side of the surface of the bottom plate 212. Moreover, the top of the air collector 21 is provided with an air-extraction inlet 214 for being in connection with an air-extraction device 26. The inlet 214 is located away from the position overhead the elongate air-extraction slot 22. In implementation, the air-extraction device 26 can be a drawing fan, an air blower, or other fluid mechanisms capable of drawing air.

In implementation, the air collector 21 also can be a substantially L-shape casing. As shown in FIG. 3, the elongate air-extraction slot 22 faces downwards and obliquely at an angle. Alternatively, as shown in FIG. 4, the elongate air-extraction slot 22 faces in a direction away from the rear end surface 24 of the air collector 21.

The long left upright plate 3 is substantially rectangular and its top is fixedly disposed below the left lateral surface of the air collector 21, so that it is extended downwards from the position below the left lateral surface of the air collector 21 to have the long left upright plate 3 and the elongate air-extraction slot 22 substantially perpendicular to each other. Besides, a curved first guiding part 31 is provided at the right side of the front end of the long left upright plate 3. The horizontal width W of the long left upright plate 3 is no less than the horizontal distance W1 from the rear end 131 of the air-generation device 13 to the wall 11. In other words, the long left upright plate will cover at least part of the left lateral surface of the air-generation device 13. In addition, the height H of the long left upright plate 3 is no less than the height H1 from the top of the counter 12 to the bottom of the long left upright plate 3.

The long right upright plate 4 and the long left upright plate 3 are symmetrically provided at the left and right sides of the air collector 21 respectively. The top of the long right upright plate 4 is fixedly provided below the right lateral surface of the air collector 21, so that it is extended downwards from the position below the right lateral surface of the air collector 21 to have the long right upright plate 4 and the elongate air-extraction slot 22 substantially perpendicular to each other. Besides, a curved second guiding part 41 is provided at the left side of the front end of the long right upright plate 4. The horizontal width of the long right upright plate 4 is no less than the horizontal distance from the rear end 131 of the air-generation device 13 to the wall 11. In other words, the long right upright plate 4 will cover at least part of the right lateral surface of the air-generation 13. In addition, the height of the long right upright plate 4 is no less than the height from the top of the counter 12 to the bottom of the long right upright plate 4.

Consequently, a first air supply space 27 in the shape of substantially rectangular is formed below the front end surface of the long left upright plate 3 and the front end of the left lateral surface of the air-extraction hood 2. Besides, a second air supply space 28 in the shape of substantially rectangular is formed below the front end surface of the long right upright plate 4 and the front end of the right lateral surface of the air-extraction hood 2. Moreover, a third air supply space 29 in the shape of substantially rectangular is formed between the bottom of the left upright plate 3 and the left side of the counter 12, while a fourth air supply space 30 in the shape of substantially rectangular is formed between the bottom of the right upright plate 4 and the right side of the counter 12.

Thereby, as shown in FIGS. 5 and 6, when the present invention is fixed onto the wall and the air-generation device 13 begins to generate soot or other harmful gases, by the operation of the air-extraction device 26 the elongate air-extraction slot 22 begins to draw air upwards. By means of high-speed air extraction of the elongate air-extraction slot 22, an oblique airflow forms below the front end of the air collector 21, so as to carry upwards the soot or other harmful gases produced by the air-generation device 13. After passing the space 211 inside the air-collector 21, the soot or other harmful gases are then exhausted by the air-extraction device 26. Because the air-extraction inlet 214 of the air-extraction device 26 is located away from the position overhead the elongate air-extraction slot 22, the accumulated waste oil will attach to the surface of the bottom plate 212 rather than drip through the elongate air-extraction slot 22. Moreover, by encircling the peripheries of the elongate air-extraction slot 22 with the oil barrier frame 213, it is able to prevent the waste oil dripping through the air-extraction slot 22. Thereby, the waste oil will flow into the oil storage box 25. It is able to resist the draft coming from lateral directions by means of the hindrance of the long left upright plate 3 and the long right upright plate 4. Consequently, the structure of above-mentioned oblique airflow will not be destroyed and an intact upwards-flowing airflow can be formed to exhaust soot and harmful gases.

Furthermore, a curved first guiding part 31 is provided at the right side of the front end of the long left upright plate 3, while a curved second guiding part 41 is provided at the left side of the front end of the long right upright plate 4. Thereby, when the air flows into the space below the air collector 21 through the first air supply space 27 and the second air supply space 28, the departing points 311, 411 of the first guiding part 31 and the second guiding part 41 will be located at more posterior positions. Consequently, it is able to reduce the backflow area produced by airflow, so as to keep the exhaust airflow flowing smoothly.

Please refer to FIG. 7, where a second embodiment of the present invention is illustrated. This embodiment differs from the first embodiment in following aspects. The counter 12 has a front end that is provided with an elongate air blow part 5. The elongate air blow part 5 has an oblique elongate air blow slot 51, the size of which is corresponding to the elongate air-extraction slot 22. The elongate air blow slot 51 is in communication with an air blower 52. By means of operation of the air blower 52, an air jet can be blown upwards at an angle through the elongate air blow slot 51 and then enters into the elongate air-extraction slot 22, so as to form an oblique air curtain 53 between the elongate air blow slot 51 and the elongate air-extraction slot 22. In implementation, a cross-flow fan or other fluid mechanisms also can be used to substitute the air blower 52.

Please refer to FIG. 8, where a third embodiment of the present invention is illustrated. This embodiment differs from the first and the second embodiments in following aspects. The range hood is directly hung above the counter 12, so that the front and rear sides of the air-extraction hood 2 are rendered open. The elongate air-extraction slot 22 is located in the midway between the front end surface and the rear end surface of the air-extraction hood 2. The horizontal width W2 of the long left upright plate 3 is no less than one-fourth the horizontal width W3 of the left lateral surface of the air-extraction hood 2, while the horizontal width of the long right upright plate 4 is no less than one-fourth the horizontal width of the right lateral surface of the air-extraction hood 2, so as to cover the left and right lateral surfaces of the air-generation device 13. As shown in FIG. 9, the rear end of the counter 12 also can be provided with another elongate air blow part 6. The elongate air blow part 6 has an elongate air blow slot 61 corresponding to the elongate air-extraction slot 22. Besides, the elongate air blow slot 61 is in communication with the air blower 52. Thereby, when an air jet is blown at an angle from the elongate air blow slot 61 and flows into the elongate air-extraction slot 22, another oblique air curtain 62 can be formed between the elongate air blow slot 61 and the elongate air-extraction slot 22.

Either a single or dual air curtains, formed in the absence or presence of the air blow parts 5, 6, are capable of carrying steadily and upwards the soot or other harmful gases into the air-extraction hood 2 and exhaust them by means of the operation of the air-extraction device 26.

In order to view several horizontal and vertical planes of the device of the present invention, smoke is released above the oven and then the laser-assisted smoke flow visualization technique is adopted. Attachment 1 is a picture showing the smoke in the horizontal plane and the intermediate vertical plane. As the distribution of the smoke in the vertical plane indicates, the smoke from the smoke generator first flows upwards and at an angle towards the back wall, and then is drawn into the air-extraction slot located at posterior position instead of escaping from the front. As the distribution of the smoke in the horizontal plane indicates, the smoke from the smoke generator largely gathers around the central area instead of diffusing laterally.

The effect of pollutant removal of the present invention is demonstrated by an experiment conducted in Thermal Fluid Laboratory, National Taiwan University of Science and Technology, where the tracer gas detection method is adopted. From a gas-releasing device disposed on the oven, sulfur hexafluoride (SF₆) gas is released at a constant concentration and a constant speed. At the distant end of the duct of the air-extraction hood, the concentration and the flow speed of the sulfur hexafluoride gas are measured in order to calculate the capture efficiency (η), which is defined as “the SF₆ gas volume flowing through per unit time divided by the SF₆ gas volume released by the gas-releasing device per unit time” measured at the distant end of the duct of the air-extraction hood.

The first test is a static test. In this test, air-extraction hoods are respectively located at different heights (H) from the counter. Under the condition that the flow velocity of the draft in ambient environment (V_(draft)) is very slow (about 0.03 m/s), the capture efficiency of five kinds of range hoods is respectively measured, where above range hoods include: (1) a conventional range hood; (2) a conventional range hood together with a slot provided at the front end of the counter for blowing air upwards; (3) a conventional range hood provided with a protection plate respectively at its left and right lateral sides; (4) an air-curtain type range hood; and (5) the range hood of the present invention. The results are shown in FIG. 10. It is evident that the capture efficiency of the first three kinds of range hoods (the conventional range hood, the conventional range hood together with a slot provided at the front end of the counter for blowing air upwards, and the conventional range hood provided with a protection plate respectively at its left and right lateral sides) is far below than that of the last two kinds (the air-curtain type range hood and the range hood of the present invention). Moreover, the capture efficiency of the range hood of the present invention is higher than that of the air-curtain type range hood. This phenomenon is more obvious especially when the height of the range hood is higher than 0.5 meter.

The second test is a test for measuring the capacity of resisting draft in ambient environment. In this test, the air-extraction hood is disposed at the height of 0.6 meter from the counter. Besides, drafts with different flow velocities (V_(draft)) are provided at a distance of two meters from the range hoods of above five kinds and are blown at an angle of forty-five degrees towards the range hoods. The capture efficiency of the five kinds of the range hoods is respectively measured. The results are shown in FIG. 11. It is evident that the capture efficiency of the first three kinds of range hoods (the conventional range hood, the conventional range hood together with a slot provided at the front end of the counter for blowing air upwards, and the conventional range hood provided with a protection plate respectively at its left and right lateral sides) is far below than that of the last two kinds (the air-curtain type range hood and the range hood of the present invention). Moreover, the capture efficiency of the range hood of the present invention is higher than that of the air-curtain type range hood. Especially, the present invention is even more advantageous when the velocity of the draft is higher than 0.2 m/s. The capture efficiency of the present invention may still remain or only slightly decrease even the velocity of the draft is as fast as 1 m/s. In contrast with the range hood according to the present invention, when the draft is gradually becoming stronger, the capture efficiency of the other four kinds of range hoods will decrease rapidly to an unacceptable extent. When the draft is blown at other angles, similar results are obtained.

Please refer to FIG. 12, where a fourth embodiment of the present invention is illustrated. In this embodiment, the long left upright plate 3 is fixed at the position below the left lateral surface of the air-extraction hood 2, while the long right upright plate 4 is fixed at the position below the right lateral surface of the air-extraction hood 2. Besides, the front end of the elongate air-extraction slot 22 is provided with an elongate air blow groove 221 having an opening that faces downwards. The elongate air blow groove 221 is parallel to the elongate air-extraction slot 22 and the elongate air blow groove 221 is in communication with an air blow device 222 for blowing air downwards. In implementation, the air blow device 222 is an air blower or a cross-flow fan. As shown in FIG. 12A, the elongate air blow groove 221 further includes a left air-blow groove 2211 and right air-blow groove 2212, which are aligned and are spaced from each other. Moreover, the elongate air blow groove 221, the left air-blow groove 2211, or the right air-blow groove 2212 can be composed of plural air-blow holes arranged to be spaced with one another.

Thereby, as shown in FIG. 13, when the air-generation device 13 produces high-temperature gas, the soot will diffuse towards the front end surface 23 of the air-extraction hood 2 because of the phenomenon of gas expansion. In the meanwhile, the air blown downwards from the air blow groove 221 is not only able to prevent the leakage of the high-temperature and expanded gas through the front end of the bottom of the air-extraction hood 2, but it is also able to guide the high-temperature gas flowing into the elongate air-extraction slot 22 in order to prevent the escape of the high-temperature gas.

FIG. 14 shows a fifth embodiment of the present invention. In this embodiment, a long left upright plate 3 is fixedly provided below the middle part of the left lateral surface of the air-extraction hood 2, while a long right upright plate 4 is fixedly provided below the middle part of a right lateral surface of the air-extraction hood 2. The elongate air-extraction slot 22 has a front end and a rear end that are respectively provided with an elongate air blow groove 221 having an opening that faces downwards. The two elongate air blow grooves 221 are respectively in communication with the air blow device 222 for blowing air downwards, so as to prevent the leakage of the high-temperature gas from the front end surface 23 or the rear end surface 24 of the air-extraction hood 2. In implementation, any of the elongate air blow grooves 221 can be composed of a left air-blow groove and a right air-blow groove 2212 that are aligned and are spaced from each other. Alternatively, the elongate air blow groove 221, the left air-blow groove, and the right air-blow groove are composed of plural air-blow holes arranged to be spaced with one another.

Therefore, the present invention has following advantages:

-   1. According to the present invention, an intact upwards-flowing     airflow can be formed in order to exhaust soot and harmful gases by     means of the elongate air-extraction slot capable of drawing in air     and the long left and right plates capable of resisting the drafts     coming from lateral sides. -   2. According to the present invention, it is able to reduce the     backflow bubble entering into the space below the air-extraction     hood by providing the front ends of the long left and right plates     respectively with a curved guiding part. Thereby, the backflow     bubble will not protrude outwards, so as to prevent the diffusion of     soot. Moreover, the upwards-flowing airflow will be rendered intact     as well, so as to ensure smooth exhaustion. -   3. According to the present invention, it is able to form an intact     upwards-flowing airflow to exhaust soot and harmful gases by the     cooperation of the elongate air-extraction slot and the long left     and right upright plates. Thereby, it is of convenient use since the     range hood of the present invention can be used to replace a     conventional range hood without the need of changing other     kitchenware. -   4. According to the present invention, the air blown downwards from     the air blow groove provided at the bottom of the air-extraction     hood not only can prevent the leakage of the high-temperature and     expanded gas, but it also can guide the high-temperature and     expanded gas flowing into the elongate air-extraction slot. Thereby,     the leakage can be effectively prevented even under the condition     that the gas is in high-temperature state and draft is present.

As disclosed in the above description and attached drawings, the present invention can provide a range hood capable of resisting draft, which can hinder the drafts coming from all directions and effectively exhaust soot and harmful gases. It is new and can be put into industrial use.

Although the embodiments of the present invention have been described in detail, many modifications and variations may be made by those skilled in the art from the teachings disclosed hereinabove. Therefore, it should be understood that any modification and variation equivalent to the spirit of the present invention be regarded to fall into the scope defined by the appended claims. 

1. A range hood capable of resisting draft, a back of which is disposed onto a wall and is located above a counter, where an air-generation device is provided on the counter's top and has a rear end facing the wall; the range hood comprising: an air-extraction hood, a bottom of which is provided with an elongate air-extraction slot having an opening that faces downwards, where the elongate air-extraction slot is in communication with an air-extraction device for drawing air upwards, and the elongate air-extraction slot is located between a front end surface and a rear end surface of the air-extraction hood and is parallel to the front end surface and the rear end surface; a long left upright plate, fixedly provided below a left lateral surface of the air-extraction hood, where the horizontal width of the long left upright plate is no less than the horizontal distance from the rear end of the air-generation device to the wall, and the vertical length of the long left upright plate is no less than the height from the counter's top to a bottom of the long left upright plate; and a long right upright plate, fixedly provided below a right lateral surface of the air-extraction hood, where the horizontal width of the long right upright plate is no less than the horizontal distance from the rear end of the air-generation device to the wall, and the vertical length of the long right upright plate is no less than the height from the counter's top to a bottom of the long right upright plate.
 2. The range hood capable of resisting draft as claimed in claim 1, wherein a first air supply space is formed below a front end surface of the left upright plate and a front end of the left lateral surface of the air-extraction hood; and a second air supply space is formed below a front end surface of the right upright plate and a front end of the right lateral surface of the air-extraction hood.
 3. The range hood capable of resisting draft as claimed in claim 1, wherein a curved first guiding part is provided at a right side of the front end of the left upright plate, and a curved second guiding part is provided at a left side of the front end of the right upright plate.
 4. The range hood capable of resisting draft as claimed in claim 1, wherein the air-extraction hood includes an air collector; the air-extraction device is connected to a top of the air collector; and the elongate air-extraction slot is formed on a bottom of the air collector.
 5. The range hood capable of resisting draft as claimed in claim 4, wherein the air-extraction device is provided with an inlet for drawing in air and the inlet is located away from the position overhead the elongate air-extraction slot.
 6. The range hood capable of resisting draft as claimed in claim 5, wherein the counter has a front end provided with an elongate air blow part; the elongate air blow part has an elongate air blow slot corresponding to the elongate air-extraction slot; an air jet is blown upwards at an angle through the elongate air blow slot and enters into the elongate air-extraction slot so as to form an oblique air curtain between the elongate air blow slot and the elongate air-extraction slot.
 7. The range hood capable of resisting draft as claimed in claim 4, wherein the air collector has a bottom plate; the elongate air-extraction slot is formed on the bottom plate; and an oil barrier frame is provided on the bottom plate and encircles the elongate air-extraction slot.
 8. The range hood capable of resisting draft as claimed in claim 1, wherein a front end of the elongate air-extraction slot is provided with an elongate air blow groove having an opening that faces downwards; the elongate air blow groove is in communication with an air blow device for blowing air downwards; the elongate air-extraction slot and the elongate air blow groove are provided between the front end surface and the rear end surface of the air-extraction hood and are parallel to the front end surface and the rear end surface.
 9. The range hood capable of resisting draft as claimed in claim 8, wherein the air blow groove includes a left air-blow groove and a right air-blow groove that are aligned and are spaced from each other.
 10. A range hood capable of resisting draft, provided above a counter, where an air-generation device is provided on the counter's top; the range hood comprising: an air-extraction hood, a bottom of which is provided with an elongate air-extraction slot having an opening that faces downwards, where the elongate air-extraction slot is in communication with an air-extraction device for drawing air upwards, and the elongate air-extraction slot is located in the midway between a front end surface and a rear end surface of the air-extraction hood and is parallel to the front end surface and the rear end surface; a long left upright plate, fixedly provided below the middle part of a left lateral surface of the air-extraction hood, where the horizontal width of the long left upright plate is no less than one-fourth the horizontal width of the left lateral surface of the air-extraction hood so as to cover the left lateral surface of the air-generation device, and the vertical length of the long left upright plate is no less than the height from the counter's top to a bottom of the long left upright plate; and a long right upright plate, fixedly provided below the middle part of a right lateral surface of the air-extraction hood, where the horizontal width of the long right upright plate is no less than one-fourth the horizontal width of the right lateral surface of the air-extraction hood so as to cover the right lateral surface of the air-generation device, and the vertical length of the long right upright plate is no less than the height from the counter's top to a bottom of the long right upright plate.
 11. The range hood capable of resisting draft as claimed in claim 10, wherein the counter's top has a front end and a rear end both of which are respectively provided with an elongate air blow part; each elongate air blow part has an elongate air blow slot corresponding to the elongate air-extraction slot for blowing an air jet upwards at an angle; the blown air jet is then drawn into the elongate air-extraction slot so as to form two corresponding oblique air curtains between the elongate air-extraction slot and two elongate air blow slots.
 12. The range hood capable of resisting draft as claimed in claim 11, wherein a front end and a rear end of the elongate air blow slot are respectively provided with an elongate air blow groove having an opening that faces downwards; the elongate air blow groove is in communication with an air blow device for blowing air downwards; and the elongate air blow grooves are respectively parallel to the elongate air-extraction slot.
 13. The range hood capable of resisting draft as claimed in claim 12, wherein the air blow groove includes a left air-blow groove and a right air-blow groove that are aligned and are spaced from each other. 